Hydrocracking of hydrocarbon feedstocks is often used to convert lower value hydrocarbon fractions into higher value products, such as conversion of vacuum gas oil (VGO) feedstocks to diesel fuel and lubricants. Typical hydrocracking reaction schemes can include an initial hydrotreatment step, a hydrocracking step, and a post hydrotreatment step. After these steps, the effluent can be fractionated to separate out a desired diesel fuel and/or lubricant oil basestock.
One method of classifying lubricating oil basestocks is that used by the American Petroleum Institute (API). API Group II basestocks have a saturates content of 90 wt % or greater, a sulfur content of not more than 0.03 wt % and a VI greater than 80 but less than 120. API Group III basestocks are the same as Group II basestocks except that the VI is at least 120. A process scheme such as the one detailed above is typically suitable for production of Group II and Group III basestocks from an appropriate feed.
U.S. Pat. No. 6,884,339 describes a method for processing a feed to produce a lubricant base oil and optionally distillate products. A feed is hydrotreated and then hydrocracked without intermediate separation. An example of the catalyst for hydrocracking can be a supported Y or beta zeolite. The catalyst also includes a hydro-dehydrogenating metal, such as a combination of Ni and Mo. The hydrotreated, hydrocracked effluent is then atmospherically distilled. The portion boiling above 340° C. is catalytically dewaxed in the presence of a bound molecular sieve that includes a hydro-dehydrogenating element. The molecular sieve can be ZSM-48, EU-2, EU-11, or ZBM-30. Tire hydro-dehydrogenating element can be a noble Group VIII metal, such as Pt or Pd.
U.S. Pat. No. 7,371,315 describes a method for producing a lubricant base oil and optionally distillate products. A feed is provided with a sulfur content of less than 1000 wppm. Optionally, the feed can be a hydrotreated feed. Optionally, the feed can be a hydrocracked feed, such as a feed hydrocracked in the presence of a zeolite Y-containing catalyst. The feed is converted on a noble metal on an acidic support. This entire converted feed can be dewaxed in the presence of a dewaxing catalyst.
U.S. Pat. No. 7,300,900 describes a catalyst and a method for using the catalyst to perform conversion on a hydrocarbon feed. The catalyst includes both a Y zeolite and a zeolite selected from ZBM-30, ZSM-48, EU-2, and EU-11. Examples are provided of a two stage process, with a first stage hydrotreatment of a feed to reduce the sulfur content of the feed to 15 wppm, followed by hydroprocessing using the catalyst containing the two zeolites. An option is also described where it appears that the effluent from a hydrotreatment stage is cascaded without separation to the dual-zeolite catalyst, but no example is provided of the sulfur level of the initial feed for such a process.
Base stocks are commonly used for the production of lubricants, such as lubricating oils for automotives, industrial lubricants and lubricating greases. A base oil is defined as a combination of two or more base stocks used to make a lubricant composition. They are also used as process oils, white oils, metal working oils and heat transfer fluids. Finished lubricants consist of two general components, lubricating base stock and additives. Lubricating base stock is the major constituent in these finished lubricants and contributes significantly to the properties of the finished lubricant. In general, a few lubricating base stocks are used to manufacture a wide variety of finished lubricants by varying the mixtures of individual lubricating base stocks and individual additives.
According to the American Petroleum Institute (API) classifications, base stocks are categorized in five groups based on their saturated hydrocarbon content, sulfur level, and viscosity index (Table 1). Lube base stocks are typically produced in large scale from non-renewable petroleum sources. Group I, II, and III base stocks are all derived from crude oil via extensive processing, such as solvent extraction, solvent or catalytic dewaxing, and hydroisomerization. Group III base stocks can also be produced from synthetic hydrocarbon liquids obtained from natural gas, coal or other fossil resources, Group IV base stocks, the polyalphaolefins (PAO), are produced by oligomerization of alpha olefins, such as 1-decene, Group V base stocks include everything that does not belong to Groups I-IV, such as naphthenics, polyalkylene glycols (PAG), and esters.
TABLE 1APIclassificationGroup IGroup IIGroup IIIGroup IVGroup V% Saturates<90≧90≧90Polyalpha-All others% S>0.03≦0.03≦0.03olefinsnotViscosity80-12080-120≧120(PAO)belonging toIndex (VI)group I-IV
The automotive industry has been using lubricants and thus base stocks with improved technical properties for a long time. Increasingly, the specifications for finished lubricants require products with excellent low temperature properties, high oxidation stability and low volatility. Generally lubricating base stocks are base stocks having kinematic viscosity of about 3 cSt or greater at 100° C. (Kv100); pour point (PP) of about −12° C. or less; and viscosity index (VI) about 90 or greater. In general, high performance lubricating base stocks should have a Noack volatility no greater than current conventional Group I or Group II light neutral oils. Currently, only a small fraction of the base stocks manufactured today are able to meet these demanding specifications.
Group II lube base stocks have limitations in terms of the lubricant applications that they may be used in because of limitations in their viscosity. Currently, Group II lube base stocks are produced by catalytic processing to a kinematic viscosity at 100° C. of less than or equal to 17 cSt. This viscosity limitation necessitates the use of Group I base stocks or Group iv synthetic base stocks in certain lubricant applications. Also solvent extracted Group I base stocks allow for high viscosity, but at lower quality, Chemically produced Group IV synthetic base stocks (PAOs) address the viscosity and quality gap regime described above, but are significantly more expensive and compositionally narrower (i.e. paraffinic structures of specific design) than Group II base stocks.
There is a need for Group II lube base stocks via catalytic processing with improved properties, and in particular higher viscosity and improved quality (improved low temperature properties and oxidative stability).